Abstract
The Nafion, Dow and Aciplex systems – where the prime differences lies in the side-chain length – have been studied by molecular dynamics (MD) simulation under standard pressure and temperature conditions for two different levels of hydration: 5 and 15 water molecules per (H)SO3 end-group. Structural features such as water clustering, water-channel dimensions and topology, and the dynamics of the hydronium ions and water molecules have all been analysed in relation to the dynamical properties of the polymer backbone and side-chains. It is generally found that mobility is promoted by a high water content, with the side-chains participating actively in the H3O+/H2O transport mechanism. Nafion, whose side-chain length is intermediate of the three polymers studied, is found to have the most mobile polymer side-chains at the higher level of hydration, suggesting that there could be an optimal side-chain length in these systems. There are also some indications that the water-channel network connectivity is optimal for high water-content Nafion system, and that this could explain why Nafion appears to exhibit the most favourable overall hydronium/water mobility.
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Acknowledgements
This work has been supported by grants from The Swedish Research Council (VR); DB gratefully acknowledges a stipend from Fred Anderssons Stiftelse; DB and AL would also like to thank the Nordic Fuel Cell Network for financial support.
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Brandell, D., Karo, J., Liivat, A. et al. Molecular dynamics studies of the Nafion®, Dow® and Aciplex® fuel-cell polymer membrane systems. J Mol Model 13, 1039–1046 (2007). https://doi.org/10.1007/s00894-007-0230-7
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DOI: https://doi.org/10.1007/s00894-007-0230-7